2007 Volume 73 Issue 2 Pages 86-93
Pythium helicoides is an important pathogen causing root rot of several crops, especially miniature rose and kalanchoe in ebb-and-flow irrigation systems that recycle nutrient solutions. In this study, we developed a PCR detection method with species-specific primers to determine sites inhabited by P. helicoides. The primers were designed based on the sequences of the internal transcribed spacer region of rDNA. The specificity of the primers was examined using 34 species and two groups of Pythium including P. helicoides, and three species in a closely related genus. The amplification with the primers detected only P. helicoides, confirming the specificity of the primers. The PCR amplified as little as 100 fg of genomic DNA of P. helicoides. When the PCR was used with naturally infested soil, the detection limit ranged from 14 to 35 cfu/g of dry soil. When this detection method was used to investigate location of P. helicoides in commercial production of miniature rose and kalanchoe, the pathogen was detected both inside and outside the greenhouses but not in the potting soil mixture, suggesting a different source other than potting soil for pathogen contamination. There are several sources of P. helicoides to contaminat clean plant, soil and the recycling nutrient solution during culture.
